Aromatization of propane over Ga-modified ZSM-5 catalysts
-
摘要: 用离子交换法制备Ga改性ZSM-5双功能催化剂,并结合XRD、SEM、BET、NH3-TPD、Py-IR及ICP、XPS等多种技术进行表征,考察分子筛硅铝比(Si/Al)和催化剂氧化还原预处理条件对分子筛的酸性质、Ga物种的存在状态及其丙烷芳构化催化性能的影响。研究表明,硅铝比不仅可以改变分子筛的酸性,也会影响分子筛中非骨架Ga物种与分子筛表面的相互作用程度,进而影响含Ga分子筛的丙烷芳构化性能。在质量空速1.0 h-1、反应温度550℃ 下,Si/Al比为30的Ga-HZSM-5分子筛丙烷转化率和芳烃收率最高。Ga物种的引入可以提高丙烷的转化率和芳烃的选择性,并抑制烷烃、烯烃的裂解。H2还原处理,将分子筛表面Ga2O3还原为低价的Ga+和GaH+2物种,促进了Ga物种向分子筛微孔迁移;还原-氧化处理后,Ga+和GaH+2物种氧化成GaO+,占据分子筛孔道离子交换位,显著提高了催化剂的芳构化活性。Abstract: H-ZSM-5 was modified with gallium by the ion-exchange method and characterized with XRD, SEM, BET, NH3-TPD, Py-IR, ICP, and XPS techniques. The influences of the Si/Al mol ratios and the pretreatment conditions of the Ga-modified ZSM-5 ((Ga-H)-ZSM-5) on their acidity, gallium species state, and aromatization performance of propane were investigated. It was found that the Si/Al mol ratio had significant effects on the catalyst acidity and the interaction of non-framework Ga species with zeolite, and hence, the catalytic activity and selectivity for propane aromatization. At 550℃ and WHSV of 1.0h-1, (Ga,H)-ZSM-5 with a Si/Al mol ratio of 30 showed the highest catalytic activity. It was shown that Ga species improved the aromatics selectivity and inhibited cracking reactions. After being reduced in hydrogen, Ga2O3 was most likely transformed into Ga+ and GaH+2 species, and migrated into the zeolite channels. Subsequent air-oxidation treatment of the reduced (Ga,H)-ZSM-5 led to formation of GaO+ species, thus greatly increasing the aromatization activity.
-
Key words:
- propane aromatization /
- Si/Al mol ratio /
- gallium species /
- ZSM-5 molecular sieves /
- pretreatment
-
ONO Y. Transformation of lower alkanes into aromatic hydrocarbons over ZSM-5 zeolites[J]. Catal Rev: Sci Eng, 1992, 34(3): 179-226. DEHERTOG W J H, FROMEN G F. A catalytic route for aromatics production from LPG[J]. Appl Catal A: Gen, 1999, 189(1): 63-75. BHAN A, DELGASS W N. Propane aromatization over HZSM-5 and Ga/HZSM-5 catalysts[J]. Catal Rev: Sci Eng, 2008, 50(1): 19-151. CHOUDHARY V R, KINAGE A K, SIVADINARAYANA C, GUISNET M. Pulse reaction studies on variations of initial activity/selectivity of O2 and H2 pretreated Ga-modified ZSM-5 type zeolite catalysts in propane aromatization[J]. J Catal, 1996, 158(1): 23-33. CHOUDHARY T V, KINAGA A, BANERJEE S, CHOUDHARY V R. Influence of Si/Ga and Si/Al ratios on propane aromatization over highly active H-GaAlMFI[J].Catal Comm, 2006, 7(3): 166-169. GUISNET M, GNEP N S. Aromatization of short chain alkanes on zeolite catalysts[J]. Appl Catal A: Gen, 1992, 89(1): 1-30. NOWAK I, QUARTARARO J, DEROUANE E G, VEDRINE J C. Effect of H2-O2 pre-treatments on the state of gallium in Ga/H-ZSM-5 propane aromatisation catalysts[J]. Appl Catal A: Gen, 2003, 251(1): 107-120. ANUNZIATA O A, PIERELLA L B. Nature of the active sites in H-ZSM-11zeolite modified with Zn(2+) and Ga(3+)[J]. Catal Lett, 1993, 19(2/3): 143-151. 苗青, 董梅, 牛宪军, 王浩, 樊卫斌, 王建国, 秦张峰. 含镓ZSM-5 分子筛的制备及其在甲醇芳构化反应中的催化性能[J]. 燃料化学学报, 2012, 40(10): 1230-1238. (MIAO Qing, DONG Mei, NIU Xian-jun, WANG Hao, FAN Wei-bin, WANG Jian-guo, QIN Zhang-feng. Synthesis of gallium-containing ZSM- 5 molecular sieves and their catalytic performance in methanol aromatization[J]. J Fuel Chem Technol, 2012, 40(10): 1230-1238.) DOOLEY K M, CHANG C, PRICE G L. Effects of pretreatments on state of gallium and aromatization activity of gallium/ZSM-5 catalysts[J]. Appl Catal A: Gen, 1992, 84(1): 17-30. PRICE G L, KANAZIREV V. Ga2O3/HZSM-5 propane aromatization catalysts: Formation of active centers via solid-state reaction[J]. J Catal, 1990, 126(1): 267-278. MADEIRA F F, TAYEB K B, PINARD L, VEZIN H, MAURY S, CADRAN N. Ethanol transformation into hydrocarbons on ZSM-5 zeolites: Influence of Si/Al ratio on catalytic performances and deactivation rate. Study of the radical species role[J]. Appl Catal A: Gen, 2012, 443-444: 171-180. 朱华青, 翟效珍, 王建国. 第二组分改性Ga/HZSM-5催化剂芳构化性能研究[J]. 燃料化学学报, 1999, 27(S): 74-78. (ZHU Hua-qing, ZHAI Xiao-zhen, WANG Jian-guo. Study on aromatization over Ga/HZSM-5 catalysts modified by second components[J]. J Fuel Chem Technol, 1999, 27(S): 74-78.) CHOUDHARY V R, MANTRI K, SIVADINARAYANA C. Influence of zeolite factors affecting zeolitic acidity on the propane aromatization activity and selectivity of Ga/H-ZSM-5[J]. Microporous Mesoporous Mater, 2000, 37(1/2): 1-8. HAAG W O, LAGO R M, WEISZ P B. The active-site of acidic aluminosilicate catalysts[J]. Nature, 1984, 309(5969): 589-591. HENSEN E J M, GARCIA-SANCHEZ M, RANE N, MAGUSIN P C M M, LIU P H, CHAO K J, VAN SANTEN R A. In situ Ga K edge XANES study of the activation of Ga/ZSM-5 prepared by chemical vapor deposition of trimethylgallium[J]. Catal Lett, 2005, 101(1/2): 79-85. KAZANSKY V B, SUBBOTINA I R, SANTEN R A, HENSEN E J M. DRIFTS study of the chemical state of modifying gallium ions in reduced Ga/ZSM-5 prepared by impregnation: I. Observation of gallium hydrides and application of CO adsorption as a molecular probe for reduced galliumions[J]. J Catal, 2004, 227(2): 263-269. 高志贤, 程昌瑞, 谭长谕. Ga/HZSM-5催化剂中镓的状态及其分布的XPS研究[J].燃料化学学报, 1995, 23(3): 301-305. (GAO Zhi-xian, CHENG Chang-rui, TAN Chang-yu. XPS study on state and distribution of gallium in Ga/HZSM-5 catalyst[J]. J Fuel Chem Technol,1995, 23(3): 301-305.) RANE N, OVERWEG A R, KAZANSKY V B, SANTEN R A V, HENSEN E J M. Characterization and reactivity of Ga+ and GaO+ cations in zeolite ZSM-5[J]. J Catal, 2006, 239(2): 478-485. 王恒强, 张成华, 吴宝山, 任杰, 李永旺. Ga、Zn改性方法对HZSM-5催化剂丙烯芳构化性能的影响[J]. 燃料化学学报, 2010, 38(3): 576-581. (WANG Heng-qiang, ZHANG Cheng-hua, WU Bao-shan, REN Jie, LI Yong-wang. Effect of Ga and Zn modification on propylene aromatization over HZSM-5 catalysts[J]. J Fuel Chem Technol, 2010, 38(3): 576-581.) MONTES A, GIANNETTOB G. A new way to obtain acid or bifunctional catalysts V. Considerations on bifunctionality of the propane aromatizationreaction over-ZSM-5 catalysts[J]. Appl Catal A: Gen, 2000, 197(1): 31-39. PIDKO E A, HENSEN E J M, VAN SANTEN R A. Dehydrogenation of light alkanes over isolated gallyl ions in Ga/ZSM-5 zeolites[J]. J Phys Chem, 2007, 111(35): 13068-13075. AUSAVASUKHI A, SOOKNOI T. Tunable activity of HZSM-5 with H2 treatment: Ethane dehydrogenation[J]. Catal Comm, 2014, 45(1): 63-68.
点击查看大图
计量
- 文章访问数: 522
- HTML全文浏览量: 19
- PDF下载量: 465
- 被引次数: 0